This undated file photo provided by the family shows Danvers High School teacher Colleen Ritzer, whose body was found behind the school on Oct. 22. / Family photo via AP

by USA TODAY

by USA TODAY

BOSTON (AP) - A Massachusetts teen admitted killing his 24-year-old math teacher but denied sexually assaulting her, police said while requesting a search warrant to see if the boy memorialized the crime on his cellphone.

Philip Chism, 15, is accused of raping and killing Danvers High School teacher Colleen Ritzer in October after she asked him to stay after school for help. He has pleaded not guilty to charges of murder and aggravated rape.

In a search warrant affidavit filed by state Trooper Steven Buccheri, police say Chism made the admission while they were interviewing him at the Danvers police station.

Chism, with his mother present, waived his Miranda rights and agreed to talk, police said. At the time, investigators were searching the woods near the school but had not yet found Ritzer's body.

"Chism admitted murdering Colleen Ritzer. During the course of the interview Chism denied having committed a sexual assault or any sexual touching of Ritzer whatsoever," Buccheri wrote in the affidavit.

Buccheri said police want to search Chism's phone because they believe they could find evidence of the killing on it.

"Based on my training and experience and the experiences of others that assisted in the investigation â?¦ I know that it is not unusual for individuals involved in homicides, particularly sexually violent homicides, to memorialize their victims' deaths through photographic, audio and or video media for further humiliation of the victim or later viewing, for guilt relief or for enjoyment," Buccheri wrote.

Chism's attorney, Denise Regan, declined to comment on the affidavit, which was filed Friday in Salem Superior Court.

Buccheri said that when police asked Chism about his cellphone, he said he had destroyed both his phone and Ritzer's phone and threw them into a wooded area.

When asked why he had destroyed the phones, Chism responded, "I destroyed them so that you would be unable to locate or track me due to the GPS capabilities of the phone," according to the affidavit.

Buccheri said police are skeptical of Chism's explanation because "it is widely understood that GPS may be disabled without destruction of the phone itself." He said it seems likely to police that Chism destroyed the phone "in order to hide incriminating evidence contained on it."

Ritzer's body was found in woods near the school with her throat slit and a note reading, "I hate you all."

Chism, who was 14 at the time of Ritzer's death, had recently moved to Danvers from Clarksville, Tenn.

In addition to murder, he was charged with aggravated rape for allegedly sexually assaulting Ritzer with a stick. An Essex County grand jury indicted him Friday on a second count of aggravated rape for forcibly having sexual intercourse with Ritzer.

In court documents released in November, police describe surveillance video they say shows Chism following Ritzer into a school bathroom, wearing gloves and a hood. He is also allegedly seen pulling a recycling barrel through the school and outside. A recycling barrel was found near Ritzer's body.

Chism is scheduled to be arraigned on the new charge Thursday in Salem.

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